This invention relates generally to an apparatus and method for monitoring a surgical tourniquet system to detect a hazard. The invention relates more particularly, but not by way of limitation, to a hazard monitor having means to detect that a pneumatic cuff of an electrically powered surgical tourniquet system is pressurized when electrical power required for operation of one or more components of the system is not supplied to the components, and to detect whether the cuff is pressurized when an operator attempts to interrupt the supply of the electrical power required for the operation of the system.
Surgical tourniquet systems are commonly used facilitate surgery by stopping the flow of arterial blood into a limb for a period of time sufficient for the performance of a surgical procedure, thereby allowing the surgical procedure to be performed in a dry and bloodless surgical field.
Published medical literature indicates that every usage of a surgical tourniquet necessarily causes some injury to the nerve, muscle and soft tissue in the limb beneath the cuff and distal to the cuff. To minimize the nature and extent of such injuries, tourniquet operators attempt to minimize the level of cuff pressure employed to establish and maintain a bloodless surgical field distal to the cuff. Also to minimize tourniquet-related injuries, tourniquet operators attempt to minimize the duration of tourniquet cuff pressurization. Cuff pressurization for an unnecessarily long period of time is hazardous because it is well established in the medical literature that the probability and severity of tourniquet-related injury to a patient""s limb increase as the duration of tourniquet application increases.
Surgical tourniquet systems of the prior art generally include a pneumatic cuff for encircling a patient""s limb at a location proximal to the surgical site, a source of pressurized gas and an instrument pneumatically connected to the cuff and the source for supplying gas to the cuff at a regulated pressure.
In some tourniquet systems of the prior art, the source of pressurized gas is a tank or hospital gas supply, while in other prior art systems an electrically powered air pump is integrated into the instrument. Some surgical tourniquet instruments known in the prior art incorporate electrically powered components including electronic pressure transducers, microprocessors, displays and audiovisual alarms. Although a few types of prior-art surgical tourniquet instruments having no electrically powered components are still in use, most of the surgical tourniquet instruments in common use at present are electrically powered in whole or in part.
One type of tourniquet instrument known in the prior art that is partially powered by electricity is the Electromedics TCPM Tourniquet Cuff Pressure Monitor (Electromedics Inc., Englewood, Colo.). This instrument includes an electrically powered display component for displaying the cuff pressure set by an operator, an electrically powered elapsed time clock to allow an operator to monitor cuff inflation time, a non-electrical pneumatic switch component for allowing an operator to inflate and deflate the cuff, and a non-electrical pressure regulator for supplying gas to the cuff at a pressure near the set pressure. An electrical power switch on the instrument controls the supply of power to the electrical components from a battery within the instrument when an operator turns on an electrical power switch on the instrument. The Electromedics instrument does not incorporate an electrically powered pump and instead requires that either a gas tank or a centralized hospital gas supply be employed as the source of pressurized gas.
The prior-art Electromedics instrument is designed so that, when a pressurized tourniquet cuff is no longer required near the end of a surgical procedure, an operator can first deflate the cuff using the non-electrical pneumatic switch component and the operator can then turn off power to the electrical components by using the electrical power switch. However, if an operator erroneously turns off the electrical power at some point during a surgical procedure and does not depressurize the cuff by using the separate pneumatic switch, then the cuff remains pressurized near a pressure regulated by the non-electrical pressure regulator while the electrical pressure display is unpowered and blank. This error may create a serious hazard for the patient if an untrained or inexperienced operator erroneously assumes that the cuff has been deflated because the pressure display is blank, and as a result the cuff remains pressurized for an extended period of time. Cuff pressurization for an unnecessarily long period of time is hazardous because it is well established that the probability and severity of tourniquet-related injuries to a patient""s limb increase as the duration of tourniquet application increases.
A tourniquet instrument known in the prior art that is completely powered by electricity is that of McEwen as described in U.S. Pat. No. B1 4,469,099, which is herein incorporated by reference. McEwen ""099 describes a surgical tourniquet system that includes both an instrument that is electrically powered and an electrically powered air pump incorporated into the instrument as the source of pressurized gas. McEwen ""099 is operable from power supplied by an external AC supply supplemented by an internal battery and includes the following electrically powered components: an operator interface for allowing an operator to set the tourniquet cuff pressure and the anticipated period of time of cuff pressurization; switches to allow the operator to initiate pressurization and depressurization of the cuff; a cuff pressure display for allowing the operator to set the cuff pressure and monitor the actual cuff pressure; a microprocessor-controlled pressure regulator for regulating the cuff pressure near the set pressure; and a time display for allowing the operator to specify a surgical time and monitor the elapsed time during which the cuff has been pressurized.
McEwen ""099 also includes a variety of electrically powered audiovisual alarms for warning the operator of certain hazardous conditions that may exist during operation, including warning of any cuff over-pressurization, cuff under-pressurization or an excessive period of cuff pressurization. If the external AC power supply to McEwen ""099 is unexpectedly interrupted while the cuff is pressurized, the internal battery continues to provide power to the displays and alarms but the pressure regulator ceases operation and pneumatic valves in the instrument seal off the pressurized cuff to retain the pressure in the cuff for as long as possible or until external AC power is restored and normal operation can resume. Thus in the event of an interruption of external AC power during use in surgery, McEwen ""099 prevents hazards for the patient such as the unanticipated flow of arterial blood into the surgical field during a procedure, the loss of large amounts of blood, and in some cases the loss of intravenous anesthetic agent retained in the limb distal to the cuff. However, an unusual type of hazard may arise if the operator erroneously turns off the electrical power switch of the instrument without first deflating the tourniquet cuff, and then does not pneumatically disconnect the cuff from the instrument and remove the cuff from the patient""s limb for an extended period of time. Turning off the electrical power switch of McEwen ""099 interrupts the supply of electrical power from both the external AC supply and the internal battery. Thus in the event of such operator errors, without the supply of any electrical power, the cuff pressure display and the time display of McEwen ""099 go blank and the audiovisual alarms are not functional, and an untrained or inexperienced operator may erroneously assume that the cuff has been deflated because the displays are blank. McEwen ""099 does not produce an audiovisual alarm to alert the operator to the hazard that the tourniquet cuff might remain pressurized and apply pressure to the patient""s limb for a prolonged period of time after interruption of the electrical power to the tourniquet instrument.
Other surgical tourniquet systems known in the prior art are entirely powered from an external AC power supply and have no internal supplementary battery as in McEwen ""099. In the event of an interruption of power to these other prior-art systems during surgery, such as might arise from a disconnection of the AC supply or an operator error, any pressure and time displays included in such instruments go blank, any audio-visual alarms are non-functional, and the pressurized cuff is sealed off pneumatically to prevent the above-mentioned types of hazards that would otherwise arise for the patient if the cuff were to immediately depressurize upon power interruption. However, none of these prior-art systems produce an audiovisual alarm to alert the operator to the hazard that the tourniquet cuff might remain pressurized for a prolonged period of time after power interruption.
Some prior-art tourniquet instruments have a xe2x80x9csoftxe2x80x9d electrical power switch, typically implemented as a momentary contact membrane switch or a low current momentary pushbutton switch. Such a xe2x80x9csoftxe2x80x9d electrical power switch does not directly control the supply of electrical power to the operational components of the tourniquet instrument but acts to control other electrical components that directly control the supply of electrical power required for operation of the tourniquet instrument. For example, each of the prior-art A.T.S. 2000 and A.T.S. 750 tourniquet instruments manufactured by Zimmer Patient Care Division (Dover, Ohio) includes a xe2x80x9csoftxe2x80x9d electrical power switch which produces an interruption of electrical power required for operation of the instrument only after the operator has initiated the power interruption by actuating the xe2x80x9csoftxe2x80x9d power switch.
No surgical tourniquet system or monitoring apparatus is known in the prior art that can detect the presence of a pressurized pneumatic cuff of a surgical tourniquet system when electrical power required for proper operation of the surgical tourniquet system is not supplied to the system. Furthermore, no electrically powered tourniquet instrument is known in the prior art that can prevent an operator from interrupting the supply of the electrical power required for the operation of the tourniquet instrument if the operator initiates an interruption of the electrical power while a pneumatic cuff connected to the tourniquet instrument is pressurized.